Prior art workers have provided various adjustment mechanisms for varying the cutting diameter of a boring tool and these are illustrated in following listed patents:
U.S. Pat. No. 3,391,585 issued July 9, 1968; PA1 U.S. Pat. No. 3,433,104 issued Mar. 18, 1969; PA1 U.S. Pat. No. 3,625,625 issued Dec. 7, 1971; PA1 U.S. Pat. No. 3,738,767 issued June 12, 1973; PA1 U.S. Pat. No. 3,744,924 issued July 10, 1973; PA1 U.S. Pat. No. 3,749,508 issued July 31, 1973; PA1 U.S. Pat. No. 3,853,422 issued Dec. 10, 1974; PA1 U.S. Pat. No. 3,918,826 issued Nov. 11, 1975; PA1 U.S. Pat. No. 4,162,867 issued July 31, 1979; PA1 U.S. Pat. No. 4,260,303 issued Apr. 7, 1981.
An adjustable collapsing tap and an adjustable threading die are described in U.S. Pat. No. 909,749 issued Jan. 12, 1909 and U.S. Pat. No. 992,903 issued May 23, 1911.